Book/Report

FZJ-2016-05817

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Berechnung des Wärmetransportes durch eine waagerechten porösen Ringspalt infolge Leitung, Strahlung und Konvektion bei variablen Stoffwerten

Tebroke, T. ; Achenbach, E.FZJ*

1992
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Please use a persistent id in citations: http://hdl.handle.net/2128/12673

Report No.: Juel-2586

Abstract: The distribution of velocity and temperature in porous media is usually calculated by applying the Darcy law and the Boussinesq approximation. This implies that all properties are set constant except the density in the buoyancy terms. This is approximately true, if temperature differences are small in the area of interest. Nevertheless, in a hot gas duct with internal insulation important temperature differences occur between the inner and the outer wall. The present work therefore investigates the influence of temperature-dependent properties on the calculated results. In particular, the contribution of radiation to the thermal conductivity was studied for a high-temperature fibrous insulation. Measurements of the thermal producticity in a vacuum show that the specific extinxtion coefficient is a practicable property to describe radiation in fibrous media. Solving the equations of continuity, momentum and energy with variable properties yields heat transfer coefficients which are up to 20 % higher than those calculated by using the Boussinesq approximation. An attempt is sometimes made to improve the results from Boussinesq's approximation byusing the temperature-dependent thermal conductivity. It is shown in this paper that this leaeds to even lower heat transfer coefficients and therefore does not represent an improvement in accuracy,

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Contributing Institute(s):

1. Publikationen vor 2000 (PRE-2000)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

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Database coverage:

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